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Maund J.R.,Copenhagen University | Maund J.R.,University of California at Santa Cruz | Craig Wheeler J.,University of Texas at Austin | Wang L.,Texas A&M University | And 6 more authors.
Astrophysical Journal | Year: 2010

We report two spectropolarimetric observations of SN 2005hk, which is a close copy of the "very peculiar" SN 2002cx, showing low peak luminosity, slow decline, high ionization near peak, and an unusually low expansion velocity of only about 7000 km s-1. Further to the data presented by Chornock et al., at -4 days before maximum, we present data of this object taken on 2005 November 9 (near maximum) and November 23 (+ 2 weeks) that show the continuum and most of the spectral lines to be polarized at levels of about 0.2%-0.3%. At both epochs the data correspond to the Spectropolarimetric Type D1. The general low level of line polarization suggests that the line-forming regions for most species observed in the spectrum have a similar shape to that of the photosphere, which deviates from a spherical symmetry by <10%. In comparison with spectropolarimetry of Type Ia and corecollapse SNe at similar epochs, we find that the properties of SN 2005hk are most similar to those of Type Ia SNe. In particular, we find the low levels of continuum and line polarization to indicate that the explosion mechanism is approximately spherical, with homogeneous ejecta (unlike the chemically segregated ejecta of CCSNe). We discuss the possibility that SN 2005hk was the result of the pure deflagration of a white dwarf and note the issues concerning this interpretation. © 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A. Source

Maund J.R.,Copenhagen University | Maund J.R.,University of California at Santa Cruz | Hoflich P.,Florida State University | Patat F.,Hemisphere | And 6 more authors.
Astrophysical Journal Letters | Year: 2010

We present a compilation of the geometry measures acquired using optical and IR spectroscopy and optical spectropolarimetry to probe the explosion geometry of Type Ia supernovae (SNe Ia). Polarization measurements are sensitive to asymmetries in the plane of the sky, whereas line profiles in nebular phase spectra are expected to trace asymmetries perpendicular to the plane of the sky. The combination of these two measures can overcome their respective projection effects, completely probing the structures of these events. For nine normal SNe Ia, we find that the polarization of Si ii λ6355 at 5 days before maximum (pSiII) is well correlated with its velocity evolution (ν̇ SiII), implying that ν̇ SiII is predominantly due to the asymmetry of the SNe. We find only a weak correlation between the polarization of SiII and the reported velocities (νneb) for peak emission of optical FeII and NiII lines in nebular spectra. Our sample is biased, with polarization measurements being only available for normal SNe that subsequently exhibited positive (i.e., redshifted) νneb. In unison these indicators are consistent with an explosion in which the outer layers are dominated by a spherical oxygen layer, mixed with an asymmetric distribution of intermediate-mass elements. The combination of spectroscopic and spectropolarimetric indicators suggests a single geometric configuration for normal SNe Ia,with some of the diversity of observed properties arising from orientation effects. © 2010 The American Astronomical Society. All rights reserved. Source

Reichardt C.L.,University of California at Berkeley | Stalder B.,Harvard - Smithsonian Center for Astrophysics | Bleem L.E.,University of Chicago | Montroy T.E.,Case Western Reserve University | And 94 more authors.
Astrophysical Journal | Year: 2013

We present a catalog of galaxy cluster candidates, selected through their Sunyaev-Zel'dovich (SZ) effect signature in the first 720 deg2 of the South Pole Telescope (SPT) survey. This area was mapped with the SPT in the 2008 and 2009 austral winters to a depth of ∼18 μKCMB-arcmin at 150 GHz; 550 deg2 of it was also mapped to ∼44 μK CMB-arcmin at 95 GHz. Based on optical imaging of all 224 candidates and near-infrared imaging of the majority of candidates, we have found optical and/or infrared counterparts for 158, which we then classify as confirmed galaxy clusters. Of these 158 clusters, 135 were first identified as clusters in SPT data, including 117 new discoveries reported in this work. This catalog triples the number of confirmed galaxy clusters discovered through the SZ effect. We report photometrically derived (and in some cases spectroscopic) redshifts for confirmed clusters and redshift lower limits for the remaining candidates. The catalog extends to high redshift with a median redshift of z = 0.55 and maximum confirmed redshift of z = 1.37. Forty-five of the clusters have counterparts in the ROSAT bright or faint source catalogs from which we estimate X-ray fluxes. Based on simulations, we expect the catalog to be nearly 100% complete above M 500 ≈ 5 × 1014 M h -1 70 at z ≳ 0.6. There are 121 candidates detected at signal-to-noise ratio greater than five, at which the catalog purity is measured to be 95%. From this high-purity subsample, we exclude the z < 0.3 clusters and use the remaining 100 candidates to improve cosmological constraints following the method presented by Benson et al. Adding the cluster data to CMB + BAO + H 0 data leads to a preference for non-zero neutrino masses while only slightly reducing the upper limit on the sum of neutrino masses to ∑m ν < 0.38 eV (95% CL). For a spatially flat wCDM cosmological model, the addition of this catalog to the CMB + BAO + H 0 + SNe results yields σ8 = 0.807 ± 0.027 and w = -1.010 ± 0.058, improving the constraints on these parameters by a factor of 1.4 and 1.3, respectively. The larger cluster catalog presented in this work leads to slight improvements in cosmological constraints from those presented by Benson et al. These cosmological constraints are currently limited by uncertainty in the cluster mass calibration, not the size or quality of the cluster catalog. A multi-wavelength observation program to improve the cluster mass calibration will make it possible to realize the full potential of the final 2500 deg2 SPT cluster catalog to constrain cosmology. © 2013. The American Astronomical Society. All rights reserved.. Source

Williamson R.,University of Chicago | Benson B.A.,University of Chicago | High F.W.,University of Chicago | Vanderlinde K.,McGill University | And 87 more authors.
Astrophysical Journal | Year: 2011

The South Pole Telescope (SPT) is currently surveying 2500deg2 of the southern sky to detect massive galaxy clusters out to the epoch of their formation using the Sunyaev-Zel'dovich (SZ) effect. This paper presents a catalog of the 26 most significant SZ cluster detections in the full survey region. The catalog includes 14 clusters which have been previously identified and 12 that are new discoveries. These clusters were identified in fields observed to two differing noise depths: 1500deg2 at the final SPT survey depth of 18μK arcmin at 150GHz and 1000deg2 at a depth of 54μK arcmin. Clusters were selected on the basis of their SZ signal-to-noise ratio (S/N) in SPT maps, a quantity which has been demonstrated to correlate tightly with cluster mass. The S/N thresholds were chosen to achieve a comparable mass selection across survey fields of both depths. Cluster redshifts were obtained with optical and infrared imaging and spectroscopy from a variety of ground- and space-based facilities. The redshifts range from 0.098 ≤ z ≤ 1.132 with a median of z med = 0.40. The measured SZ S/N and redshifts lead to unbiased mass estimates ranging from 9.8 × 10 14 M® h -1 70 ≤ M 200(ρ mean) ≤ 3.1 × 1015 M® h -1 70. Based on the SZ mass estimates, we find that none of the clusters are individually in significant tension with the ΛCDM cosmological model. We also test for evidence of non-Gaussianity based on the cluster sample and find the data show no preference for non-Gaussian perturbations. © 2011. The American Astronomical Society. All rights reserved. Source

Benson B.A.,University of Chicago | De Haan T.,McGill University | Dudley J.P.,McGill University | Reichardt C.L.,University of California at Berkeley | And 107 more authors.
Astrophysical Journal | Year: 2013

We use measurements from the South Pole Telescope (SPT) Sunyaev-Zel'dovich (SZ) cluster survey in combination with X-ray measurements to constrain cosmological parameters. We present a statistical method that fits for the scaling relations of the SZ and X-ray cluster observables with mass while jointly fitting for cosmology. The method is generalizable to multiple cluster observables, and self-consistently accounts for the effects of the cluster selection and uncertainties in cluster mass calibration on the derived cosmological constraints. We apply this method to a data set consisting of an SZ-selected catalog of 18 galaxy clusters at z > 0.3 from the first 178 deg2 of the 2500 deg2 SPT-SZ survey, with 14 clusters having X-ray observations from either Chandra or XMM-Newton. Assuming a spatially flat ΛCDM cosmological model, we find the SPT cluster sample constrains σ8(Ωm/0.25)0.30 = 0.785 ± 0.037. In combination with measurements of the cosmic microwave background (CMB) power spectrum from the SPT and the seven-year Wilkinson Microwave Anisotropy Probe data, the SPT cluster sample constrains σ8 = 0.795 ± 0.016 and Ωm= 0.255 ± 0.016, a factor of 1.5 improvement on each parameter over the CMB data alone. We consider several extensions beyond the ΛCDM model by including the following as free parameters: the dark energy equation of state (w), the sum of the neutrino masses (Σm ν), the effective number of relativistic species (N eff), and a primordial non-Gaussianity (f NL). We find that adding the SPT cluster data significantly improves the constraints on w and Σm ν beyond those found when using measurements of the CMB, supernovae, baryon acoustic oscillations, and the Hubble constant. Considering each extension independently, we best constrain w = -0.973 ± 0.063 and the sum of neutrino masses Σm ν < 0.28 eV at 95% confidence, a factor of 1.25 and 1.4 improvement, respectively, over the constraints without clusters. Assuming a ΛCDM model with a free N eff and Σm ν, we measure N eff = 3.91 ± 0.42 and constrain Σm ν < 0.63 eV at 95% confidence. We also use the SPT cluster sample to constrain f NL = -220 ± 317, consistent with zero primordial non-Gaussianity. Finally, we discuss the current systematic limitations due to the cluster mass calibration, and future improvements for the recently completed 2500 deg2 SPT-SZ survey. The survey has detected ∼500 clusters with a median redshift of ∼0.5 and a median mass of ∼2.3 × 10 14 M h -1 and, when combined with an improved cluster mass calibration and existing external cosmological data sets will significantly improve constraints on w. © 2013. The American Astronomical Society. All rights reserved.. Source

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